The invention relates to dishwashers, particularly to plastic tub dishwashers.
The use of plastic as a tub material offers many advantages. Among these advantages are more economical tub construction, increased tub life and lower weight.
To exploit these advantages to the fullest extent, it is necessary to develop tub and hardware mounting structures that further minimize weight, material and manufacturing costs while at the same time providing sufficient support and structural stiffness to prevent premature tub failure.
U.S. Pat. No. 4,359,250 discloses a plastic dishwasher tub and frame assembly and is incorporated in its entirety herein by reference. The patent sets forth a plastic tub supported by a metal frame. The frame comprises a main frame portion made from a piece of U-channel bent in a U-shape supporting the front portion of the tub and two U-channels bent into right angles supporting the rear portion of the tub. One end of each right-angle bent U-channel is attached at the base of the jamb at each side of the door frame and the other end is retained in a pocket formed in the bottom of the tub at respective sides of the tub. A piece of angle iron is attached between the two right-angle bent U-channels so that it abuts the tub bottom to provide additional support for the rear of the tub.
Fabrication of the support for the rear of the tub requires three separate pieces. The two right-angle bent U-channel pieces must be formed and the angle iron attached between them. Fabrication of the frame members also requires the forming of a length of U-channel. The bending of a length of U-channel into a U-shape is difficult because of the tendency of the sides of the U to bend or buckle during the forming operation. Furthermore, there is a problem in securing the plastic tub to the metal frame because the softness of the plastic as compared to metal requires substantial contact area to avoid deformation of the plastic in the contact areas.
It is well known in the art to provide a front-loading dishwasher with a downwardly opening door having counterbalance springs. The door is hinged to the door frame by hinge arms on the sides of the door. These hinge arms have extensions that serve as levers for mounting one end of the counterbalance springs. To limit the travel of the door in the open position (typically a horizontal position), prior art dishwashers employ a rigid tab or similar projection from the door frame as a door stop to limit the hinged rotation of the hinge arms.
This tab or projection as well as the door frame must possess substantial resistance to the bending moment produced when the hinge arm swings against the tab. This is particularly true when a user rolls a rack full of dishes out onto the open door. This requires the tab or projection and at least an area on the door frame about the tab or projection to be of substantial thickness.